FIGS. 1 and 2 are schematic sectional views of light emitting diodes in which a fluorescent substance is applied in accordance with a prior art. FIG. 1 is a sectional view of a conventional top-type light emitting diode and FIG. 2 is a sectional view of a conventional lamp-type light emitting diode.
Referring to FIG. 1, the light emitting diode comprises a substrate 10 with first and second lead terminals 30 and 35 formed thereon, a light emitting diode chip 20 mounted on the substrate 10, and a reflecting portion 40 formed on the substrate to surround the light emitting diode chip 20. The light emitting diode chip 20 is electrically connected to the first and second lead terminals 30 and 35 through wires 70. A molding portion 60 is formed on the light emitting diode chip 20 by filling a liquid epoxy resin or the like into the reflecting portion 40 and thermally curing the resin for a predetermined time so as to protect the light emitting diode chip 20. Further, a fluorescent substance 50 for absorbing light emitted from the light emitting diode chip 20 and performing wavelength conversion of the light into respective different wavelengths is mixed in the molding portion 60.
Referring to FIG. 2, the light emitting diode comprises a first lead terminal 80 with a reflecting portion 40 at an upper end thereof and a second lead terminal 85 spaced apart by a predetermined distance from the first lead terminal 80. Further, a light emitting diode chip 20 is mounted inside the reflecting portion 40 of the first lead terminal 80, and a molding portion 60 is formed on the light emitting diode chip 20 by applying a liquid epoxy resin or the like and thermally curing the resin for a predetermined time so as to protect the light emitting diode chip 20. Further, a fluorescent substance 50 for absorbing light emitted from the light emitting diode chip 20 and performing wavelength conversion of the light into respective different wavelengths is mixed in the molding portion 60.
When the fluorescent substance is applied as described above, the fluorescent substance with a higher specific gravity precipitates due to a difference in specific gravity between the fluorescent substance and the epoxy resin with a relatively lower specific gravity during the predetermined time when the liquid epoxy resin is cured. A difference in concentration within the liquid epoxy resin occurs due to such precipitation of the fluorescent substance, and thus, there is a problem with color reproducibility because light emitted from the light emitting diode chip is not uniform. Further, since a color speckle is produced, a great amount of fluorescent substance should be contained in the molding portion to express a uniform color, resulting in degradation of light emitting efficiency. Furthermore, since the fluorescent substance is not uniformly distributed, there is a problem in that the color of light emitted from the light emitting diode varies depending on an angle at which the light emitting diode is viewed.
FIGS. 3 and 4 are schematic sectional views of light emitting diodes in which a fluorescent substance is applied in accordance with another prior art. The light emitting diodes shown in FIGS. 3 and 4 are different from those shown in FIGS. 1 and 2 in that a mixture of a fluorescent substance and a resin is dotted with a predetermined thickness to encapsulate a light emitting diode chip and a molding portion is then formed thereon. However, remaining components of the light emitting diodes shown in FIGS. 3 and 4 are identical to those of the light emitting diodes shown in FIGS. 1 and 2.
Referring to FIG. 3, in the light emitting diode, the mixture of fluorescent substance and resin is dotted on the light emitting diode chip 20, and the molding portion 65 is formed inside a reflecting portion 40. Referring to FIG. 4, the fluorescent substance 50 is injected only inside the reflecting portion 40, and a transparent epoxy resin is used for the peripheral molding portion 65 to enhance the transmissivity of light emitted from the light emitting diode chip 20.
In the case where the mixture of fluorescent substance and resin is applied as described above, the mixture may flow laterally. Thus, there is a problem in that the distance between the light emitting diode and the fluorescent substance varies and thus a color may not be uniformly expressed and two or more different colors may be produced depending on a light emitting region. Further, in case of FIG. 4, the luminous efficiency of light considerably decreases due to interference between the light emitting diode chip and the reflecting portion.
FIG. 5 is a schematic sectional view of a light emitting diode in which a fluorescent substance is applied in accordance with a further prior art. The light emitting diode of FIG. 5 further comprises a guide member 90 for preventing a mixture of fluorescent substance and resin from flowing outside a substrate or lead terminals when the mixture of fluorescent substance and resin is dotted on a light emitting diode chip. However, since an additional process should be added to attach the guide member 90, a fabricating process becomes complicated, resulting in increased production costs. Further, there is a problem in that luminous efficiency decreases and a great amount of fluorescent substance is consumed due to the guide member.